Integrated Information Theory and Isomorphic Feed-Forward Philosophical Zombies
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Any theory amenable to scientific inquiry must have testable consequences. This minimal criterion is uniquely challenging for the study of consciousness, as we do not know if it is possible to confirm from the outside whether or not a physical system knows what it feels like to have an inside - a challenge referred to as the "hard problem" of consciousness. To arrive at a theory of consciousness, the hard problem has motivated theorists to develop phenomenological approaches that adopt assumptions of what properties consciousness has based on first-hand experience and, from these, derive the physical processes that give rise to these properties. A leading theory adopting this approach is Integrated Information Theory (IIT), which assumes our subjective experience is a "unified whole", subsequently yielding a requirement for physical feedback between components as a necessary condition for consciousness. Here, we develop a mathematical framework to assess the validity of this assumption by testing it in the context of isomorphic physical systems with and without feedback. We demonstrate the existence of strictly feed-forward "philosophical zombies" capable of emulating not only the input-output behavior of their integrated counterparts but also an isomorphic sequence of internal state transitions. Indeed, the only difference between the integrated system (Φ>0) and its isomorphic zombie counterpart (Φ=0) is a permutation of the binary labels used to instantiate the functional states of the system. This proves that isomorphic logical architectures can exist that realize the exact same mathematical computation using different internal representations. For any quantitative theory of consciousness, including IIT, to be robust against this argument it must either justify a connection between consciousness and a particular internal representation or be invariant under isomorphisms.
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